Method and apparatus for maintaining uniform tensile stress in strip



Apnl 12, 1966 w. ROBERTS 3,245,241

METHOD AND APPARATUS FOR MAINTAINING UNIFORM v TENSILE STRESS IN S'I'RIPFiled July 22, 1963 2 Sheets-Sheet 1 l/Vl/EN TOR. WILLIAM L. ROBERTS A Iromey Aprll 12, 1966 w. ROBERTS 3,245,241

METHOD AND APPARATUS FOR MAINTAINING UNIFORM TENSILE STRESS IN STRIPFiled July 22, 1963 2 Sheets-Sheet 2 W/LL/AM L. ROBERTS Wfljd;

A Harney United States Patent 3,245,241 METHOD AND APPARATUS FORMAINTAINING UNIFORM TENSILE STRESS IN STRIP William L. Roberts,Murrysville, Pa., assignor to United States Steel Corporation, acorporation of Delaware Filed July 22, 1963, Ser. No. 296,685 Claims.(Cl. 72-9) This invention relates to a method and apparatus formaintaining uniform tensile stress at opposite sides of a metal stripduring a rolling operation.

As metal strip is rolled, it is pulled through work rolls under tension.The rolls reduce the strip in stages to a predetermined thickness. Ifthe tensile stress at opposite sides of the strip is not uniform duringrolling, the strip maly be defective. One form of defect likely to occuris camber, which refers to a sideways bending; that is, one side edge ofa cambered strip is convex and longer than the other. When metal stripis used in coil form, for example in the manufacture of containers, itis particularly important that the strip be free of camber. It is alsopossible that nonuniform tensile stresses in strip may causemetallurgical defects, since the strip is not worked uniformly.

An object of the present invention is to provide a method and apparatusfor determining whether tensile stresses are uniform at opposite sidesof a strip during rolling, thus furnishing information needed to avoiddefects caused by nonuniform stresses.

A further object is to provide a method and apparatus of the foregoingtype which automatically adjust a striprolling stand to maintain uniformstress in opposite sides of a strip.

A more specific object is to provide an improved method and apparatusfor preventing nonuniformities in stress at opposite sides of a stripduring rolling in which the ratio of tension to thickness is measured ateach side, the two ratios are compared, and the screwdown motors of theroll stand are operated automatically to eliminate any diiferences inthe ratios.

In the drawing:

FIGURE 1 is a diagrammatic perspective view of a roll stand equippedwith an apparatus for maintaining uniform stress in accordance with myinvention;

FIGURE 2 is a schematic wiring diagram of a ratiocomputing deviceembodied in the apparatus; and

FIGURE 3 is a schematic wiring diagram of a ratiocomparing and controldevice embodied in the apparatus.

FIGURE 1 shows diagrammatically a conventional strip-rolling stand whichincludes upper and lower work rolls 10 and 12, screws 13 and 13a at theleft and right operatively connected with the rolls for regulating theirspacing, reversible screwdown motors 14 and 14a, and gearing 15 and 15aconnecting the motors with the respective screws. Since the mechanicalconnection between the screws and rolls is conventional, no showing isdeemed necessary. A cooperating tensioning device 16, for exampleanother set of rolls, pulls a continuous metal strip S through the workrolls 10 and 12.

In accordance with the present invention, I mount thickness gages 17 and17a in locations to measure the strip thickness at the left and rightsides respectively, preferably about halfway between each edge of thestrip and the center line, and on the exit side of the work rolls 10 and12. These gages can be of conventional construction, preferably of theX-ray or equivalent radiation type, and they generate electric signalsproportional to the strip thickness. I connect the gages in a way thatthe potential of the signals therefrom increases as the strip becomesthicker, as known in the art. The strip also runs over a tension roller18 journaled in bearings 19 and 19a at the left and right respectivelyand located on the exit side of the work rolls 10 and 12 but ahead ofthe tensioning device 16. Bearings 19 and 19a are mounted on posts 20and 20a, which carry conventional electric strain gages 21 and 21arespectively. Tension in strip S applies compressive loads to posts 20and 20a. The magnitude of load on each post, and hence the deformationor strain, are proportional to the tension in each side of the strip.The electrical resistance of each strain gage is at a maximum when thestrip is free of tension and there is no compressive load on the posts.The greater the tension, the less the resistance.

I connect the thickness gage 17 and strain gage 21 to a ratio-computingdevice 22, hereinafter described. This device continuously computes theratio of tension to thickness in the left half of the strip. Similarly Iconnect thickness gage 17a and strain gage 21a to a ratio-computingdevice 22a, which computes this ratio for the right half. The ratio oftension to thickness in each half of the strip is an approximation ofthe tension per unit of cross-sectional area in that half, or thetensile stress therein. If the two ratios are unequal, the stress in thetwo sides of the strip is not uniform. I connect the two ratio-computingdevices 22 and 22a to a ratio-comparing and control device 23,hereinafter described, and I connect this device to the two screwdownmotors 14 and 14a. Whenever the ratios become unequal, the controldevice completes circuits to operate the two motors in oppositedirections. Thus the work rolls 10 and 12 move a little closer togetherat one end and farther apart at the other. The thickness of the stripdecreases slightly at one side and increases at the other until the tworatios become equal.

FIGURE 2 shows in more detail one example of a circuit I can use in theratio-computing device 22. The circuit includes a bridge, the arms ofwhich are the strain gage 21, a variable resistor 24 and two fixedresistors 25 and 26. I connect a power supply 27 and a conventionalamplifier 28 across opposite terminals of the bridge in the usual way. Iconnect the respective output terminals of the amplifier to a ground 29and to one end of a series of resistors 30, 30a 3017 etc. of equalvalue. The ratiocomputing device also includes a conventional digitalvoltmeter 31 to which I connect the thickness gage 17. One example of asuitable digital voltmeter is available commercially from Non-LinearSystems, Inc., Del Mar, California, as the NLS Model 481 and isdescribed in a printed publication by the supplier, Catalog 356. Imechanically connect the digital voltmeter to a rotary switch arm 52,which is engageable with a succession of contacts 33, 33a, 3%, etc.connected between the resistors 39, 30a, 3012, etc. I connect arm 32 toa ground 34 through a resistor 35, which is relatively small as comparedwith resistors30, 30a etc. I connect an output conductor 36 between arm32 and resistor 35.

I "adjust resistor 24 to a'value equal to that of the strain gage whenthere is no tension in strip S. Under this condition the bridge isbalanced and no current flows through the amplifier. As the strip istensioned and the fresistance offered by the strain gage diminishes, thebridge becomes unbalanced and current commences to flow. The greater thetension, the greater the current. The digital voltmeter 31 positions therotary switch arm 32 in accordance with the thickness of the strip asmeasured by "gage 17. The thicker the strip, the greater the number thestress in the left half of the strip. The ratio-computing device 22aoperates similarly, except that the connections to the output terminalsof the amplifier are reversed to produce a voltage signal of theopposite polarity in its output conductor 36a. In the interest ofsimplicity, I have not repeated the showing.

FIGURE 3 shows in more detail one example of a circuit I can use in theratio-comparing and control device 23. The device includes a D.-C.voltage amplifier 39 and four relays A, B, C and D. I connect the twoconductors 36 and 36a from the ratio-comparing device 22 and 22a to acommon terminal 37 through resistors 38 and 38a. I connect terminal 37to one input terminal of amplifier 39 and connect the other inputterminal of the amplifier to a ground 40. The amplifier has outputterminals 41 and 42, to which I connect the coils of relays A and B inseries with a rectifier 43. Similarly I connect the coils of relays Cand D to these output terminals in series with a rectifier 44 arrangedto conduct current in the opposite direction from rectifier 43. As longas the ratios of tension to thickness in the two sides of strip S areequal, the potential on conductors 36 and 36a are equal and opposite.The voltage amplifier 39 transmits no signal, and all the relays remaindeenergizied. If the ratio on the left side of the strip exceeds that onthe right side, the potential on conductor 36 becomes greater and theoutput terminal 41 becomes positive with respect to 42, whereupon relaysA and B are energized. Similarly, if the ratio on the right side exceedsthat on the left, relays C and D are energized.

Relay A has two front or normally open contacts A and A and two back ornormally closed contacts A and A The other relays have similar contactsdesignated by the same subscripts. I connect the control device to anoutside D.-C. power source via lines 45 and 46. A conductor 47 extendsfrom line 45 to one side of each front contact A B C and D Similarly aconductor 48 extends from line 46 to one side of each front contact A BC and D I connect the other sides of each contact of relays A and C tothe terminals of the left screwdown motor 14, and the other sides ofeach contact of relays B and D to the terminals of the right screwdown14a. When relays A and B are energized, motor 14 is energized in adirection to move the left ends of the work rolls and 12 farther apart,and motor 14a is energized in a direction to move the right ends closertogether. Thus the thickness of the right side of the strip diminishesand the thickness on the left side increases until the ratios of tensionto thickness become equal. The reverse action occurs when relays C and Dare energized. Preferably I also connect an indicator 49 across theoutput terminals 41 and 42 to shown any inequality in the ratios.Optionally I can use this indicator to adjust the roll spacing by manualactuation screwdown motors, and omit the relays which actuate thesemotors automatically.

I connect a manually operable double-throw, multicontact switch 50between lines and 46 and the back contacts of the four relays. Normallya spring 51 holds switch in an open position. Closing the switch in onedirection energizes both screwdown motors 14 and 14a in the samedirection to move the work rolls 10 and 12 closer together. Closing theswitch the other way energizes both motors to move the rolls fartherapart.

From the foregoing description it is seen that my invention affords asimple method and apparatus for maintaining uniform tensile stress inopposite sides of a strip during rolling. In this manner I successfullyavoid camher in the strip. While my invention may cause slightvariations in the thickness of the strip from side to side, this is amuch less serious defect than camber. Normally specifications allowstrip thickness to vary up to plus or minus 10 percent from the nominalthickness.

While I have shown and described only a single embodiment of myinvention, it is apparent that modifications may arise. Therefore, I donot wish to be limited to the disclosure set forth but only by the scopeof the appended claims.

I claim:

1. In a rolling operation in which metal strip is pulled through a setof work rolls under tension to reduce its thickness, a method ofmaintaining uniform tensile stress in opposite sides of the stripcomprising determining the ratio of tension in the strip to thethicknessthereof at each side of the center line on the exit side of the rolls,and adjusting the thickness at each side of the strip to furnish equalratios.

2. In a rolling operation in which metal strip is pulled through a setof work rolls under tension to reduce its thickness, a method ofmaintaining uniform tensile stress in opposite sides of the stripcomprising measuring the thickness of the strip and the tension thereinat each side of the center line on the exit side of the rolls, computingfrom these measurements the ratio of tension to thickness at each sideof the strip, comparing the two ratios, and adjusting the thickness ateach side to furnish equal ratios.

3. In a rolling operation in which metal strip is pulled through a setof work rolls under tension to reduce its thickness, a method ofmaintaining uniform tensile stress in opposite sides of the stripcomprising measuring the thickness of the strip at locations abouthalfway between each side edge and the center line on the exit side ofthe rolls, measuring the tension in each side of the strip, computingthe ratio of tension to thickness at each side, and adjusting the rollsto bring them closer together at one end and farther apart at the otherwhenever the ratios are unequal, thereby changing the thickness at eachside of the strip to furnish equal ratios.

4. In a strip-rolling mill which includes a set of Work rolls,adjustable means operatively connected with said rolls at each endforvarying the spacing therebetween, and a cooperating tensioning devicespaced from said rolls for pulling metal strip therethrough undertension, the combination therewith of an apparatus for maintaininguniform tensile stress in opposite sides of the strip comprising meansfor computing the ratio of tension in the strip to the thickness thereofat each side of the center line on the exit side of said rolls, andmeans operatively connected with said computing means and with saidadjustable means for operating the latter when the ratios are unequaland thereby adjusting the strip thickness to furnish equal ratios.

5. In a strip-rolling mill which includes a set of work rolls,adjustable means operatively connected with said rolls at each end forvarying the spacing therebetween, and a cooperating tensioning devicespaced from said rolls for pulling metal strip therethrough undertension, the combination therewith of an apparatus for maintaininguniform tensile stress in opposite sides of the strip comprising meansfor measuring the thickness of the strip at each side of the center lineon the exit side of said rolls, means for measuring the tension in thestrip at each side of the center line, means operatively connected withsaid measuring means for computing the ratio of tension to thickness ateach side, and means operatively connected with said computing means forcomparing the two ratios and thereby determining whether the stress isuniform at opposite sides.

6. In a strip-rolling mill which includes a set of work rolls,adjustable means operatively connected with said rolls at each end forvarying the spacing therebetween, and a cooperating tensioning devicespaced from said rolls for pulling metal strip therethrough undertension, the combination therewith of an apparatus for maintaininguniform tensile stress in opposite sides of the strip comprising meansfor measuring the thickness of the strip at each side of the center lineon the exit side of said rolls, means for measuring the tension in thestrip at each side of the center line, means operatively connected withsaid measuring means for computing the ratio of tension to thickness ateach side, means operatively connected with said computing means forcomparing the two ratios, and a control device operatively connectedwith said comparing means and with said adjustable means for operatingthe latter when the ratios are unequal and thereby adjusting the stripthickness to furnish equal ratios.

7. In a strip-rolling mill which includes a set of work rolls,adjustable means operatively connected with said rolls at each end forvarying the spacing therebetween, and a cooperating tensioning devicespaced from said rolls for pulling metal strip therethrough undertension, the combination therewith of an apparatus for maintaininguniform tensile stress in opposite sides of the strip comprising a pairof gages positioned to measure the thickness of the strip on the exitside of said rolls at locations about halfway between each side edge ofthe strip and the center line, means for measuring the tension in thestrip at each side of the center line, means operatively connected Withsaid gages and with said measuring means for computing the ratio oftension to thickness at each side, means operatively connected with saidcomputing means for comparing the two ratios, and a control deviceoperatively connected with said comparing means and with said adjustingmeans for operating the latter to bring said rolls closer together atone end and farther apart at the other whenever the ratios are unequal,thereby changing the thickness at each side of the strip to furnishequal ratios.

8. A combination as defined in claim 7 in which said tension-measuringmeans includes a tension roller over which the strip runs on the exitside of said work rolls, bearings in which opposite ends of said tensionroller are journaled, posts supporting said bearings, and electricstrain gages mounted on said posts.

9. A combination as defined in claim 7 in which said computing means foreach side includes a bridge circuit, one of the arms of said circuitbeing a strain gage the electric resistance of which varies With thetension in the corresponding side of the strip, an amplifier connectedacross said bridge for transmitting current varying with the tension, aseries of resistors connected to said amplifier, a digital voltmeterconnected to the thickness gage on the corresponding side of the strip,an arm operatively connected with said voltmeter for cutting in a numberof resistors varying with the strip thickness, a resistor in series withsaid arm, and a conductor connected with said last-named resistor fortransmitting a voltage signal proportional to the ratio.

10. A combination as defined in claim 7 in which said comparing meansincludes a D.-C. voltage amplifier connected to receive voltage signalsof opposite polarity from the computing means for each side of thestrip, and said control device includes relays for establishing currentpaths which operate said adjustable means, and rectifiers in series withsaid relays and said amplifier for selectively energizing said relayswhen the voltage signals are unequal.

References Cited by the Examiner UNITED STATES PATENTS 3,006,225 10/1961 Mamas 721j2 3,078,747 2/1963 Pearson 729 3,081,651 3/1963 Roberts729 CHARLES W. LANHAM, Primary Examiner.

1. IN A ROLLING OPERATION IN WHICH METAL STRIP IS PULLED THROUGH A SETOF WORK ROLLS UNDER TENSION TO REDUCE ITS THICKNESS, A METHOD OFMAINTAINING UNIFORM TENSILE STRESS IN OPPOSITE SIDES OF THE STRIPCOMPRISING DETERMINING THE RATIO OF TENSION IN THE STRIP TO THETHICKNESS THEREOF AT EACH SIDE OF THE CENTER LINE ON THE EXIT SIDE OFTHE ROLLS, AND ADJUSTING THE THICKNESS AT EACH SIDE OF THE STRIP TOFURNISH EQUAL RATIOS.
 4. IN A STRIP-ROLLING MILL WHICH INCLUDES A SET OFWORK ROLLS, ADJUSTABLE MEANS OPERATIVELY CONNECTED WITH SAID ROLLS ATEACH END FOR VARYING THE SPACING THEREBETWEEN, AND A COOPERATINGTENSIONING DEVICE SPACED FROM SAID ROLLS FOR PULLING METAL STRIPTHERETHROUGH UNDER TENSION, THE COMBINATION THEREWITH OF AN APPARATUSFOR MAINTAINING UNIFORM TENSILE STRESS IN OPPOSITE SIDES OF THE STRIPCOMPRISING MEANS FOR COMPUTING THE RATIO OF TENSION IN THE STRIP TO THETHICKNESS THEREOF AT EACH SIDE OF THE CENTER LINE ON THE EXIT SIDE OFSAID ROLLS, AND MEANS OPERATIVELY CONNECTED WITH SAID COMPUTING MEANSAND WITH SAID ADJUSTABLE MEANS FOR OPERATING THE LATTER WHEN THE RATIOSARE UNEQUAL AND THEREBY ADJUSTING THE STRIP THICKNESS TO FURNISH EQUALRATIOS.